1. Field of the Invention
The present invention relates to hydraulic power systems with electrically operated valves that control fluid flow to hydraulically drive actuators, and more particularly to mechanisms that detect faults occurring in such systems.
2. Description of the Related Art
A wide variety of machines have moveable elements that are driven by a hydraulic actuator, such as a cylinder and piston arrangement. For example, a telehandler has a tractor on which a telescopic boom is mounted with a load carrier pivotally attached to the remote end of the boom. The telescopic boom and the load carrier are moved with respect to the tractor by hydraulic actuators. The flow of fluid to and from each hydraulic actuator is governed by a valve assembly controlled by the machine operator.
There is a present trend away from manually operated hydraulic valves toward electrical controls and the use of solenoid valves. For example, the operator sitting in a cab of the telehandler manipulates a joystick that produces an electrical signal designating a velocity desired for an associated element, such as the boom or load carrier. An electronic controller responds to the joystick signal by applying electric current to the valve assembly so that the proper amount of fluid is supplied to the respective hydraulic actuator to move the machine component at the desired velocity.
It is important to detect velocity faults or errors between the actual velocity of a machine component and the desired velocity. Such errors may result in an unsafe operation of the machine and thus require corrective action. On a telehandler, for example, it is desirable to detect a sudden drop of the boom which could occur due to a burst hose or other event. Upon detection of a velocity error, corrective action, such as operating a secondary isolation valve, can be performed.
Therefore, it is desirable to detect a velocity error of a machine component in order to take proper corrective action. However, such detection must be sufficiently robust to avoid erroneously declaring a fault condition because taking corrective action during normal machine action also may have adverse consequences.